The present invention relates to the extraction of electrical or mechanical energy or coherent radiation from chemical reactions occurring on the surface of a catalyst before thermal equilibrium has been reached by the forms of the released energy.
Recent experimental observations have revealed clues to various catalytic processes occurring: 1) during the 0.01 picosecond time interval during which chemical reactants form bonds with the surface of a catalyst, causing the emission of charge carriers, such as electrons and holes; 2) during the picosecond time interval during which reactants adsorb and lose energy in quantum steps after becoming trapped at a potential well between an adsorbate and a catalyst surface, producing electronic friction, charge carrier currents and phonon emission; and 3) during the nanosecond and longer time intervals during which reaction intermediates and products radiate electromagnetic energy, either while trapped on a catalyst surface or immediately after escaping it. These processes entail three energy releasing processes, namely: 1) charge carrier emission (electrons and holes), 2) phonon emission and 3) photon emission.
The discovery of these pre-equilibrium emissions provides new pathways to convert the high grade chemical energy available during pre-equilibrium phases into useful work. The term xe2x80x9cpre-equilibriumxe2x80x9d refers to the period, however brief, during which the products of reactions have not yet come to thermal equilibrium. These products include energy emissions, such as charge carriers; high frequency phonons normally associated with the optical branch lattice vibrations and with acoustic branch vibrations of similar wavelength and energy; and excited state chemical product species.
Prior to the discovery of these rapid energy emission pathways, the energies resulting from a catalytic process, such as the heat of adsorption and the heat of formation, were considered to be heat associated with an equilibrium condition. Indeed, after tens of femtoseconds, emitted charge carriers have thermalized and after a few to hundreds of picoseconds, emitted phonons have thermalized.
In an exemplary embodiment of the present invention, the emissions of charge carriers, such as electron-hole pairs, generated by chemical activity and reactions on or within catalyst surfaces, clusters or nanoclusters, are converted into electric potential. In an exemplary embodiment, semiconductor diodes such as p-n junctions and Schottky diodes formed between the catalyst and the semiconductors are used to carry out the conversion. The diodes are designed to collect ballistic charge carriers and can be Schottky diodes, pn junction diodes or diodes formed by various combinations of metal-semiconductor-oxide structures. The interlayer oxide thickness is preferably less than the particular ballistic mean free path associated with the energy loss of the appropriate charge carrier (e.g., hole or electron). The diodes are placed in contact with or near the catalyst nanolayer or nanocluster within a distance whose order of magnitude is less than approximately the mean free path of the appropriate ballistic charge carrier originating in the catalyst. In one embodiment, the diode is located adjacent to the catalyst cluster, while in a further embodiment, the diode is located under the catalyst, as a substrate.
The charge carriers travel ballistically over distances that can exceed the width of appropriately fabricated semiconductor junctions, similar to a thermionic effect. However, unlike the thermionic effect, the charge carriers in the case of the present invention need not have energy greater than the work function of the material involved. The charge carrier motion is trapped as a difference in fermi level, or chemical potential, between either side of the junction. The resulting voltage difference is indistinguishable from that of a photovoltaic collector. However, the charge carrier forces itself into the valence or conduction band and the circuit provides a counterpart hole or electron.
The present invention also provides devices and methods for converting the energy generated by catalytic reactions to mechanical motion before the energy thermalizes. In an exemplary embodiment, the converted motion is used to move a hydraulic fluid against a resisting pressure.
Recent advances in the art of quantum wells, atomically smooth superlattices and nanometer scale fabrication permit a degree of tailoring of the physical parameters to favor a particular reaction pathway (charge carrier, phonon, photon) or to enhance the efficiency of the energy collector.
The temperature of operation of a device in accordance with the present invention can be as low as hundreds of degrees Kelvin, which is much lower than the typical operational temperatures of conventional thermophotovoltaics and thermionic systems (1500 to 2500 Kelvin). Moreover, the power per mass and power per volume ultimately achievable using pre-equilibrium emissions in accordance with the present invention exceeds that of fuel cells, conventional thermo-photovoltaics, and conventional thermionic systems.
Furthermore, in comparison to fuel cells which require complex ducting, the devices of the present invention allow mixing of fuel and air in the same duct, thereby simplifying ducting requirements.
The combination of high volume and mass power density, simplicity, and lower temperature operation makes the methods and devices of the present invention competitive and uniquely useful.